a. Field of the Invention
The present invention relates to a laser diode device and, more particularly to such a laser diode device, which has an automatic power control circuit directly encapsulated in the heat sink (or submount) inside the metal cap for driving by voltage instead of current.
b. Description of the Related Art
A laser semiconductor is a kind of diode, also called as a laser diode. Unlike regular diodes, a laser diode has the function of a laser oscillator. Therefore, a laser diode has the electric properties of regular diodes and the optical property of emitting a laser light as a laser oscillator does. A laser oscillator is an object (media) that causes a laser effect. It can be seen in gas form, liquid form, or semiconductor form. Ruby laser device is a solid laser device. Helium-neon laser device is a gas form laser device that emits red laser light. Chromatic laser device is a typical liquid form laser device. These laser generating devices have a big size not less than several tens centimeters that consumes more than several tens of watts for operation. Further, a laser semiconductor is a kind of diode having the size smaller than 1 mm3. Light of about 10 mW can be obtained if a laser semiconductor allows only several +mA direct current to pass in forward bias direction. Therefore, a laser semiconductor can easily be installed in a small apparatus, for example, a CD player or optical communication device. Laser semiconductors have been intensively used in optical communication devices as light source means.
FIG. 1 shows a laser diode device according to the prior art. According to this design, the laser diode device comprises a laser diode 11. The laser diode 11 comprises a heat sink 111 holding a laser diode chip, and a metal cap 112 bonded to the heat sink 111 and internally filed with a dry gas to protect the laser diode chip. When packaged, the laser diode 11 has a diameter about 5.6 mm. Further, the heat sink 111 has three or four pins 113 extended out of the back (bottom) side. The pins 113 of the laser diode 11 are bonded to a circuit board 12, and then assembled with a mount 13, a cover 14 and a spring member 15 to form the desired laser diode device 10. The laser diode 11 of the laser diode device 10 is driven by an electric current obtained from the circuit board 12. According to this design, the circuit board 12 is provided outside the laser diode 11. After installation of the laser diode 11 in the circuit board 12, the photo output of the laser diode 11 must be regulated manually. Further, after the connection of the laser diode 11 to the circuit board 12, the size of the whole assembly is greatly increased. According to this design, the size of the laser diode device 10 is greater than 9 mm, not practical for use in certain small-size products.